Adam Brown: belief

Transcript context

…Tell me if this is just a question that doesn't make sense. Because when I was, if you try to ask somebody about the quantum many worlds, "Where are the other worlds?" right? And they're just like, "They're in Hilbert space." "Where is Hilbert space?" "No, dude, it's just a conceptual thing. Stop asking questions." Intuitively, it feels like there should be a sense in which there is some physical existence. Either that existence is in this four-dimensional space, or it's in some space that exists on the boundary. Is this just going to lead us into philosophical loops, or is there something that can be said more about it? And also, in a de Sitter space, in a world like ours, what exactly would the boundary mean? There are two components to that question. You have an intuition that if something is real, it needs to be spatially localized, and things that are delocalized in space somehow can't be real. I would say that that's not my intuition. My intuition is that there can be two completely different descriptions of the same physics, and if it's precise, neither of those is any more real than the other. Things do not need to be spatially localized. You separately asked, what would a version of "where is the boundary theory?" in de Sitter space, since there's no boundary? That is a great question that people who are trying to generalize AdS/CFT to a universe like ours, that has a positive cosmological constant, wrestle with. There's more than one proposal. Some suggest that the dual theory should live on the cosmic horizon. So, if you go 5 billion light-years, you can send information to that point and have it returned to you. But on the other hand, there are things that are 100 billion light-years away that we'll never be able to communicate with. There's a boundary between those two -- between things that we could, in principle, communicate with and things that we couldn't, in principle, communicate with. That is the cosmological horizon. Some people who are trying to do a version of holography that works in universes with a positive cosmological constant like to put the second theory there. Other people like to put it in the distant future, in the sort of infinitely distant future. That's part of the problem: where do we even put that theory? It's not like in our universe where you can just put it spatially infinitely far away and be done with it. If it's spatially finite, then we are currently at the boundary of infinite many other universes that are located, or whose center is located, elsewhere.…

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